Patent GB-869313-A (GB)
Title: Improvements in signal generating apparatus
IPC: G04C23/34
Filed: 1959-05-19
Abstract: 869,313. Electric selective-signalling systems. GENERAL TIME CORPORATION. May 19, 1959 [June 16, 1958], No. 16951/59. Class 40 (1). A signal generating system comprises a first plurality of relays having contacts thereon interconnected into a switching network leading from an input connector to a set of outgoing group selection conductors, each of said group selection conductors being connected to said input conductor for a separate combination of energized and de-energized ones of said relays, means to energize said relays in any of said combinations at any of a plurality of time intervals, a first plurality of switches, cyclically operable driving means for said switches coupled to said switches to close the same in a predetermined cyclical succession, and separate means each responsive to connection of a separate one of said group selection conductors to said input conductor to energize said driving means and to complete a circuit in parallel with the contacts of each switch of a separate combination of said switches. A selective calling system is described for selectively operating a number of remotely situated devices (such as lights, bells, and the like in a school) by means of signals superimposed on the main electric power supply cables. The controls that are to be effected in a complete week are registered by means of manually-settable pins on a number of drums having a seven-day period (see U.S.A. Specification 2,711,790, which is referred to). Additional controls, not in the normal sequence, can be effected as and when necessary by manually-controlled switches. The control drums rotate continuously, the pins in them controlling switches, and one control signal can be transmitted each minute. Each control signal, Fig. 2, comprises a start pulse, of four seconds duration, five " group selection " pulses, which are significant in combination and which select a particular group of five remote devices to be controlled, and five " circuit selection " pulses which are independently significant and which select those (one, two, three, four or five) of the remote devices in the selected group that are to respond to the following " function " pulse which can cause selected remote devices to turn on or to turn off. The actual controls set on the pin drums each contain two bits additional to those shown in Fig. 2. These are used to select one of four frequencies on which the signal shown in Fig. 2 is to be transmitted. Whenever a control is sensed on the pin drums the thirteen bits are registered, for one minute, on relays which recede the " group selection " bits to mark one of 32 line. The marked line then selects one of 32 storage relays which has pre-wired into it five bits identical to the " group selection " bits which caused it to be selected. These parallel signals are then serialized and transmitted on a selected one of four carrier frequencies to the remote devices to be controlled. Word recognition circuit, Fig. 3.-A callword comprises five " group selection " pulse positions A to E, Fig. 2, which are significant in combination, and five " circuit selection " pulse positions F to J which are significant independently of each other. Thus, each combination of pulses A to E corresponds to five-word recognition circuits, which, in turn, correspond to the five pulses F to J, and thus each call word can call from one to five-word recognition circuits. At each recognition circuit each incoming pulse is filtered from the main power line 202, 203, Fig. 3 (on which it is superimposed), amplified and applied to a relay 208. Each start pulse, Fig. 2, which is of four seconds duration, energizes a relay 212, via contacts 208-3 and 210-1, to start a 1 r.p.m. synchronous motor 215 which drives cams 210, 214, 216, 217 and 218, the later of which establishes a hold circuit for the motor. Group selection pulses are recognized by cams 217 and 214 which have projections corresponding to the " ones " and to the " zeros " respectively, of the particular group selection combination that is to be recognized and are so arranged that if a one occurs when a zero should cam 214 de-energizes relay 212 while if a zero occurs when a one should cam 217 de-energizes relay 212. Cam 217 also recognizes the particular circuit selection " one " pulse that should be present. Zeros among the circuit selection pulses are not looked for, however, as up to five-word recognition circuits may be selected by one call word. In a selected recognition circuit relay 212 remains energized for the whole duration of a call word and results in a signal being applied to either terminal 204 or 205 to turn on or turn off the device being controlled in accordance with the presence or absence of an " off " control pulse, Fig. 2.